#9 add code variant: modify FDNT initial condition to the truth value

Changes:
* Modified `SBParse` such that it takes an optional `Shear& out_shear` parameter, for cases when we want to know the shear that the `SBParse` has read.
* Added `FDNTRing_spl_true_ic.cpp`, which gives the true applied shear as the FDNT starting point, for comparison with when the starting point is random.
* Added, then deleted, `FDNTRing_spl_noisy_ic.cpp`, as it is identical to `FDNTRing_spl.cpp`.